1. Field of the Invention
This invention relates in general to an image sensing device and more particularly to an image sensing device whereby the image on an image plane such as a page or the like is read in the form of electrical signals using an array of photovoltaic conversion elements.
2. Description of the Prior Art
The conventional image sensor as above briefly described includes plural photovoltaic conversion elements consisting of photodiodes or non-crystalline or polycrystalline film etc., normally arranged in a row. These photovoltaic conversion elements generate electrical charges corresponding to the amount of incident light, i.e., the number of photons received from an image plane. These charges are stored in capacitances (interelectrode capacitance, stray wiring capacitance etc.). One terminal of each of photovoltaic conversion elements is connected to a power source. The other terminal of each of the elements is connected to a respective switching element which may be, for example, a MOS-FET. The switching elements are sequentially driven by a shift register so that they read out the charge signal stored in the capacitances. That is, the charge generated in the photovoltaic conversion elements is stored in the capacitances from the time when the switching elements are sequentially turned ON until they are again turned ON after completing the reading of one line, and this stored charge is read out when the corresponding switching elements have turned ON again. This charge which is read out is then extracted as the read-out output by means of a detector circuit.
However, in such an image sensor, the signal reading circuit that contains the switching elements is usually constructed of a monolithic integrated circuit such as a MOS-IC. In this case, the photovoltaic conversion elements and the integrated circuit are connected by conductive strips defining wiring patterns formed on the substrate. However, in the installation of the integrated circuit, these conductive strips will have to be of unequal length, with the result that the stray capacitances of these respective conductive strips will be unequal. As these stray capacitances of the conductive strips form part of the capacitances for storing the signal charge, the non-uniformity of these stray capacitances implies non-uniformity of these capacitances. This therefore results in the read-out output of the signal charges being non-uniform, giving rise to problems of instability of the image-reading sensitivity.